tritrpticin and dodecylphosphocholine

Structural changes for a series of antimicrobial peptides in various solvents were investigated by a combined approach of FTIR and CD spectroscopy. The well-characterized and potent antimicrobial peptides indolicidin and tritrpticin were studied along with several analogs of tritrpticin, including Tritrp1 (amidated analog of tritrpticin), Tritrp2 (analog of Tritrp1 with Arg-->Lys substitutions), Tritrp3 (analog of Tritrp1 with Pro-->Ala substitutions) and Tritrp4 (analog of Tritrp1 with Trp-->Tyr substitutions). All peptides were studied in aqueous buffer, ethanol and in the presence of dodecylphosphocholine (DPC) micelles. It was shown that tritrpticin and its analogs preferentially adopt turn structures in all solvents studied. The turn structures formed by the tritrpticin analogs bound to DPC micelles are more compact and more conformationally restricted compared to indolicidin. While several peptides showed a slight propensity for an alpha-helical conformation in ethanol, this trend was only strong for Tritrp3, which also adopted a largely alpha-helical structure with DPC micelles. Tritrp3 also demonstrated along with Tritrp1 the highest ability to interact with DPC micelles, while Tritrp2 and Tritrp4 showed the weakest interaction.

Topics: Amino Acid Sequence; Amino Acid Substitution; Antimicrobial Cationic Peptides; Buffers; Circular Dichroism; Dimethyl Sulfoxide; Ethanol; Micelles; Oligopeptides; Phosphorylcholine; Solvents; Spectrophotometry, Infrared; Spectroscopy, Fourier Transform Infrared; Trifluoroethanol

Tritrpticin is a member of the cathelicidin family of antimicrobial peptides. Starting from its native sequence (VRRFPWWWPFLRR), eight synthetic peptide analogs were studied to investigate the roles of specific residues in its biological and structural properties. This included amidation of the C-terminus paired with substitutions of its cationic and Phe residues, as well as the Pro residues that are important for its two-turn micelle-bound structure. These analogs were determined to have a significant antimicrobial potency. In contrast, two other peptide analogs, those with the three Trp residues substituted with either Phe or Tyr residues are not highly membrane perturbing, as determined by leakage and flip-flop assays using fluorescence spectroscopy. Nevertheless the Phe analog has a high activity; this suggests an intracellular mechanism for antimicrobial activity that may be part of the overall mechanism of action of native tritrpticin as a complement to membrane perturbation. NMR experiments of these two Trp-substituted peptides showed the presence of multiple conformers. The structures of the six remaining Trp-containing analogs bound to dodecylphosphocholine micelles showed major, well-defined conformations. These peptides are membrane disruptive and show a wide range in hemolytic activity. Their micelle-bound structures either retain the typical turn-turn structure of native tritrpticin or have an extended alpha-helix. This work demonstrates that closely related antimicrobial peptides can often have remarkably altered properties with complex influences on their biological activities.

Topics: Amino Acid Substitution; Anti-Infective Agents; Escherichia coli; Fluoresceins; Hemolysis; Humans; In Vitro Techniques; Liposomes; Magnetic Resonance Spectroscopy; Micelles; Microbial Sensitivity Tests; Models, Molecular; Oligopeptides; Phosphorylcholine; Staphylococcus aureus; Structure-Activity Relationship